Approximately 450 feet underground, below the streets of Oahu, sits a true feat of engineering: a massive, little-known tunnel, a rail car and subway named the Howling Owl and 20 massive fuel tanks the tunnel system was built to store. This is the Red Hill Underground Fuel Storage Facility, a top secret military facility built during the early 1940s for wartime use. Did you know about these Hawaii underground tunnels? Let’s take a look…

Editor’s note: Please not that this tunnel is not open to the public.

The facility was decommissioned in the 1990s, and is now considered to be one of Hawaii's greatest engineering feats, placed alongside the Hoover Dam, the Eiffel Tower, and the Panama Canal as an important historic landmark. But yet, very few people actually know much about the secret facility, and even fewer have been inside.
U.S. Pacific Fleet/Flickr
That's because tightened security after 9/11 made the underground tunnel off limits to the general public. The only pictures we could find are courtesy of the United States Navy, and civilians are almost never granted access to the facility.
Construction on the underground facility began in 1940, and was completed in 1943, as a means to protect Pearl Harbor's fuel supply in case of an attack.
U.S. Pacific Fleet/Flickr

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The impenetrable, bombproof facility is home to 20 reinforced concrete fuel tanks hollowed out of volcanic rock, each roughly the size of the 23-story Ala Moana building. Red Hill can hold approximately 252 gallons of diesel and jet fuel, and can provide fuel to Pearl Harbor, Hickam Air Force Base, and even Barbers Point Naval Air Station.
U.S. Pacific Fleet/Flickr
Located 100 feet under a ridge in Honolulu, construction on the facility continued after the Japanese attack on Pearl Harbor, and though more than 3,900 workers were involved with construction, Red Hill's existence remained classified for five decades.
Chief Mass Communication Specialist Shawn P. Eklund, U.S. Navy/Wikimedia Commons
In 1995, Red Hill was designated as a historic civil engineering landmark by the American Society of Civil Engineers.
U.S. Pacific Fleet/Flickr
Though this Hawaii underground tunnel is now known to the public, Red Hill's history is a relative mystery. It is said that dozens of fuel leaks occurred at the site throughout the last seen decades, and while testing suggests that the water found near the facility is safe for drinking, the jury is still out on the environmental impact of this massive, secret underground tunnel system.

For a more comprehensive lesson about the tunnels history and construction, be sure to watch this video uploaded by the U.S. Fleet Forces Command in 2011, less than 20 years after the site was declassified.

Did you know about this impressive fuel storage facility hiding underneath the island? Learn about another little-known little know feat of engineering and wartime relic, the Waikiki Natatorium, here.

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Hawaii Underground Tunnels

Sarah M. | August 07, 2022

What are some other secret places in Hawaii?

Unlike the Hawaii underground tunnels, there is a secret beach along the Kaua’i’s Coast that folks can - and should! - visit and explore! There’s a secret beach in Hawaii right along Kaua’i’s coast that you have to visit if you love seashells. This stunning beach is hidden from view, and you need to hike a little bit to get there, but it is worth it if stunning sunsets and beautiful, sandy beaches are your thing. Secret Beach on Kaua’i’s coastline is a gorgeous spot that’s on the quieter side, and easy to explore. There are so many wonderful things to do here, including hunt for seashells. Put this spot on your list the next time you want to hunt for seashells away from the crowds!

What are some remote and untouched places in Hawaii?

The Na Pali Coast, a pristine piece of rugged Kauai coastline, is said to be one of the most unspoiled natural beauties in all of Hawaii: thousand foot cliffs are eroded to create vaulted valleys and hidden beaches. The erosion is the culprit behind one of the coastline’s other main features. You see, the only way to gain access is by a long, arduous hike, by boat, or via helicopter tour. And that’s not for lack of trying – roads were once attempted, but as one of the most rapidly changing shorelines in the world, it was a futile attempt. This is a place that most certainly belongs on your Hawaii bucket list!

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